The present invention relates to improvements in a conductivity cell utilized in a particle study device. An example of such a conductivity cell is disclosed in Russian Pat. No. 274,474.
In the field of particle study devices it is common for a liquid electrolyte containing particles to be moved through a sensing zone. Each particle traversing the sensing zone generates an electrical signal. However, changes in the conductivity of the electrolyte alter the signals. In the well known COULTER particle study device the sensing zone includes an aperture located in the wall of a vessel situated within another vessel, sensing electrodes are situated on either side of the aperture and mechanisms are provided for causing, and for monitoring the amount of, fluid flow through the aperture. As a particle flows through the aperture it causes a change in the electric field and the electric current between the sensing electrodes. This change is picked up by a signal-detecting circuit and the signal produced thereby is amplified and referred to as a particle pulse. (The mark COULTER is a registered trademark, No. 995,825 of Coulter Electronics, Inc. of Hialeah, Flordia.)
Heretofore it has been proposed to insert another electrode into one of the bodies of liquid electrolyte so as to form a resistance between that electrode and with either one of the sensing electrodes or with a fourth electrode inserted in one of the bodies of electrolyte. The resistance between the third electrode and either one of the sensing electrodes or the fourth electrode is then connected into the electrical sensing circuitry for the particle analyzing device in such a manner as to compensate for changes in electrolyte conductivity.
According to the invention there is provided, in a particle study device wherein a liquid electrolyte containing parties is caused to traverse an electrical sensing zone of small dimensions and wherein the device has a conductivity cell including two electrodes in the electrolyte for establishing a variable resistance which is a function of the conductivity of the electrolyte and which is connected to the electrical sensing circuit including the sensing zone to provide compensation for changes in electrolyte conductivity, a conductivity cell which includes a long, narrow column of electrolyte between the conductivity cell electrodes with each of the conductivity cell electrodes being in contact with the electrolyte at one end of the column.
The conductivity cell preferably includes a long tube or tubing which may be straight or coiled and the long and narrow column of electrolyte is situated within the tubing. A conductivity cell including such a long narrow column of electrolyte provides a much larger resistance in the conductivity cell thereby to compensate better for changes in the conductivity of the electrolyte.